The objectives of the research are twofold: (1) to elucidate the genetic control mechanisms of mutagenesis in human and mammalian cells; and (2) to develop reliable in vitro assay systems for environmental mutagens and promoters. We propose (a) to develop a mutation assay system in a transformed human epithelial cell line; (b) to isolate mutagen sensitive and DNA repair or replication mutants of human or Chinese hampster cells by a combined treatment of Brdu-black light and 3H lethal incorporation by viral suicide method and by selection with inhibitors of DNA polymerase alpha or beta; and (3) to characterize these mutants genetically and biochemically. Furthermore, we will develop an assay system to screen for chemicals that eliminate metabolic cooperation in human cells. The compounds will be used to test whether they can enhance human cell transformation in vitro.